Magnetospinning apparatus for low-magnetic materials and methods of use

ABSTRACT

Embodiments of the present disclosure provide magneto-spinning apparatus, methods of use, magnetospun material (e.g., a fiber such as a low- or non-magnetic fiber), and the like.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. Provisional Application Ser. No. 62/003,682, having the title “MAGNETOSPINNING APPARATUS AND METHODS OF USE,” filed on May 28, 2014, the disclosure of which is incorporated herein in by reference in its entirety.

This application is related to co-pending application entitled “MAGNETOSPINNING APPARATUS AND METHODS OF USE”, having Ser. No. 14/723,523 filed on May 28, 2015, the disclosure of which is incorporated herein by reference.

BACKGROUND

Electrospinning is dependent on the dielectric properties of the solvent used. For example, the electric field required to obtain steady jetting increases with a decrease in the dielectric constant of the polymer-solvent system. Polycaprolactone (PCL) solution fibers with diameters below 200 nm can be electrospun only when the dielectric constant of a solvent satisfies ε_(r)>19. Below this value, the resulting fibers have diameters in the micrometer to millimeter range. Consequently, this limitation precludes the use of many polymer-solvent combinations for electrospinning nanofibers. Electrospinning of many biopolymers cannot be realized without blending with another polymer. Further, reactive spinning when a diffusion-limited chemical reaction is used to synthesize or modify polymers in spinning solutions, cannot be realized by electrospinning due to the specific physics of the process.

SUMMARY

Embodiments of the present disclosure provide magneto-spinning apparatus, methods of use, magnetospun material (e.g., a fiber such as a low- or non-magnetic fiber), and the like.

An embodiment of the present disclosure includes a magneto-spinning apparatus, comprising a device that delivers a fiber precursor material, and a magnet positioned a distance from the device, wherein the fiber precursor material is drawn to the magnet to form a fiber, wherein the device is configured to deliver the fiber precursor material and a secondary material, wherein the device is configured so that the fiber precursor material and the secondary material are adjacent one another at a tip of the device.

An embodiment of the present disclosure also includes a method of forming a fiber, comprising drawing a fiber precursor material from an aperture of a device towards a magnet positioned a distance from the aperture to form a fiber; dispensing a secondary material from a second aperture of the device so that the fiber precursor material is adjacent the secondary material; moving the magnet to extend the length of the fiber; moving the magnet so that the fiber wraps around a portion of a post positioned a distance from the magnet; and moving the magnet, post, or both so that the fiber extends from the magnet to the post, is wrapped around a portion of the post, and extends back toward the magnet.

Other apparatus, methods, features, and advantages will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional apparatus, methods, features and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects of the present disclosure will be more readily appreciated upon review of the detailed description of its various embodiments, described below, when taken in conjunction with the accompanying drawings.

FIGS. 1A-J illustrate a schematic of the magnetospinning set-up and the resulting PCL fibers.

FIG. 1A shows a polymer solution pushed through the needle while a magnet is rotating on a circular stage. Red and blue colors represent, respectively, the north and south poles of the spherical magnet.

FIG. 1B illustrates that as the magnet approaches the ferrofluid, the magnetic force attracts the droplet towards the magnet.

FIG. 1C illustrates a liquid bridge formed between the magnet and the needle.

FIG. 1D illustrates that the magnet moves away and draws the polymer fiber while the solvent evaporates. The resulting nanofibers are spooled on a reel that is attached to the opposite side of the stage.

FIGS. 1E-F are SEM and TEM images of fabricated PCL fibers with a range of diameters.

FIGS. 1G-H are photographs of approximately 2500 nanofibers, produced in 5 minutes at 500 RPM. Inset in 1H shows SEM image of aligned nanofibers.

FIG. 1I is a photograph of a magnetospinning set-up.

FIG. 1J shows rheological characterization of polymer-nanoparticle mixtures.

FIGS. 2A-I explain the magnetospinning limits. The droplet is attracted by the magnetic and a liquid bridge is stretched to form a stable nanofiber (FIG. 2A). The droplet transitions to the magnet without forming a liquid bridge (FIG. 2B). The magnet rotates too fast and the droplet is unable to attach to the magnet (FIG. 2C). FIG. 2D illustrates the phase diagram of the PCL magnetospinning process with the theoretically predicted upper and lower bounds indicated by the solid and dashed curves respectively, beyond which nanofiber spinning is prohibited. FIG. 2E illustrates the phase diagram of the PCL magnetospinning process with the theoretically predicted upper bound where nanofiber spinning is prohibited as the volume fraction φ of nanoparticles is varied. FIG. 2F shows mean diameters of the produced fibers versus angular velocity of the rotating stage. Error bars for 4% PCL fibers are smaller than the square marker. The inset demonstrates theoretical predictions based on Eq. (1). FIG. 2G shows measurements of the fiber diameter along its 25 cm length. FIG. 2H shows viscosity versus polymer concentration for PCL/chloroform/MNP solutions. Critical entanglement concentration C_(cr) was found to be 3.7% as estimated at the concentrations where there is a significant increase in viscosity. FIG. 2I shows productivity of magnetospinning method.

FIGS. 3A-F illustrate magnetospinning of alginate fibers. Two droplets are pushed through the needle next to each other—the droplet on the right is filled with Fe304, water and alginate solution, and the left droplet is filled with CaCl₂-water solution (FIG. 3A). The magnet approaches and the magnetic droplet is attracted towards the magnet (FIG. 3B). The magnetic droplet starts moving towards the magnet through the droplet with CaCl₂ solution (FIG. 3C). Ca²⁺ ions cross-link the alginate and as a result the polymer droplet can be stretched into a fiber (FIG. 3D). FIG. 3E is a schematic of the fiber spinning from the coaxial needle for electrospinning of two liquids in contact. FIG. 3F shows bright field optical microscopy images of alginate fibers.

FIGS. 4A-D demonstrate magnetospinning of non-magnetic fibers. In FIG. 4A, a droplet of PCL-chloroform solution is pushed through the needle using an automated pump. A droplet of Fe₃O₄ nanoparticles dispersed in water is placed on the PCL droplet using a second syringe. The magnetic droplet is attracted towards the magnet (FIG. 4B). The magnetic droplet jumps towards the magnet and a non-magnetic fiber is produced (FIG. 4C). FIG. 4D is an SEM image of produced fibers.

FIGS. 5A-D are SEM and TEM images of fibers produced via magnetospinning.

FIG. 5A is magnetospun Teflon© fiber. Inset shows water droplet on the mat for Teflon© fibers.

FIG. 5B shows porous non-magnetic PMMA fibers.

FIG. 5C is a poly(ethylene oxide) (PEO) fiber with embedded silver nanowire (Ag NW) (1.7 wt % of silver nanowires).

FIG. 5D is a TEM image of PEO fiber with embedded multi-walled carbon nanotubes (10 wt % of MWCNT).

FIG. 5E is an image of cells cultured on collagen-coated magnetic fibers

DETAILED DESCRIPTION

Before the present disclosure is described in greater detail, it is to be understood that this disclosure is not limited to particular embodiments described, and as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended claims.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the disclosure. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the disclosure, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure, the preferred methods and materials are now described.

As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure. Any recited method can be carried out in the order of events recited or in any other order that is logically possible.

Embodiments of the present disclosure will employ, unless otherwise indicated, techniques of chemistry, material science, and the like, which are within the skill of the art.

The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to perform the methods and use the probes disclosed and claimed herein. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in ° C., and pressure is at or near atmospheric. Standard temperature and pressure are defined as 20° C. and 1 atmosphere.

Before the embodiments of the present disclosure are described in detail, it is to be understood that, unless otherwise indicated, the present disclosure is not limited to particular materials, reagents, reaction materials, manufacturing processes, or the like, as such can vary. It is also to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting. It is also possible in the present disclosure that steps can be executed in different sequence where this is logically possible.

It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

Definitions

“Magnetospinning” is a process in which fibers (e.g., magnetic fibers) are formed from a solution or melt by streaming a material (e.g., a fiber precursor material such as a magnetic fiber precursor material) through an aperture, where a magnetic field causes the fiber precursor material to extend or bridge across a distance to a magnet to form the fiber (e.g., a magnetic fiber). Subsequently, the fiber length can be increased by streaming more fiber precursor material and moving the magnet to extend the distance of the magnet from the aperture, for example.

“Magnetospun material” is a structure or group of structures (such as fibers, webs, or the like), as a result of the magnetospinning process. This material may be natural, synthetic, or a combination of such. In an embodiment, the magnetospun material has a magnetic characteristic. In an embodiment, the magnetospun material does not have a magnetic characteristic or weakly magnetic characteristic.

“Polymer” is any natural or synthetic molecule that can form long molecular chains, such as nylons, polyethylene, polystyrene, polylactide, polyglycolide, polypropylene, polyacetylene, polyphenylene vinylene, polypyrrole, polyesters, polyurethanes, combinations of these, and blends of these.

Discussion

Embodiments of the present disclosure provide magneto-spinning apparatus, methods of use, magnetospun material (e.g., a fiber such as a magnetic fiber), and the like. Embodiments of the present disclosure are advantageous because embodiments of the present disclosure are independent of solution conductivity and do not require high-voltages and the accompanying electrical components as compared to electrospinning. In addition, the magneto-spinning apparatus is easy to set up and operate. Additional details and advantages are described herein and the examples.

In an embodiment, the magneto-spinning apparatus can include a device for delivering a fiber precursor material (e.g., a magnetic fiber precursor material) and a magnet, where the device and the magnet are a distance apart. In general, the magnetic field generated by the magnet draws a fiber precursor material towards the magnet so that the fiber precursor material contacts the magnet. In this way, the fiber precursor material can be drawn to the magnet to form a fiber (e.g., a magnetic fiber).

In an embodiment, the device can include a storage compartment for the fiber precursor material, a pump or other system to cause the fiber precursor material to flow, and an aperture. In an embodiment, the device can be a syringe, where the fiber precursor material flows out of the tip of the syringe. In an embodiment, the device can include two or more outlets where materials coming out of each outlet are adjacent one another and can be comingled with one another prior to or as the material is drawn to the magnet. In an embodiment, the device is similar to an electrospinning device but is different due to the use of a magnetic field as opposed to an electric field, thus, the requirements regarding conductivity of various components and reagents are not necessary for a magneto-spinning apparatus. As a result, the magneto-spinning apparatus is generally a less complex apparatus to build and operate.

In an embodiment, the device, magnet, and other components (e.g., post) of the magneto-spinning apparatus can be physically distinct components and could be described as a magneto-spinning system. In this regard, the magneto-spinning apparatus can include a device or structure including the device, the magnet, and other components (e.g., post). In addition, the magneto-spinning apparatus can include a magneto-spinning system where the one or more components can be physically distinct components from the other components, but can function as a unit to produce fiber. Components of the magneto-spinning apparatus and there interaction are discussed in relation to methods of forming the magnetic fiber that follows as well as in Example 1.

In an embodiment, the method of forming a magnetic fiber can include drawing a fiber (e.g., magnetic fiber) from an aperture of a device towards a magnet positioned a distance (e.g., about 0.1 to 10 mm) from the aperture to form the fiber. The fiber precursor material flows from the aperture and is attracted to the magnet. Once the fiber is formed and is in contact with the magnet, the magnet can move, while optionally simultaneously additional fiber precursor material is flowed from the aperture, to draw or extend the length of the fiber.

One or more configurations of the apparatus can be used to draw the fiber to generate a longer fiber (e.g., 1 to 50 cm) having a desired diameter (e.g., about 50 nm to 20 μm). In one embodiment, the movement of the magnet causes the fiber to wrap around a portion (e.g., outside portion) of one or more posts (e.g. reels) or other structure, where the post is positioned a distance (e.g., about 1 to 50 cm) from the magnet. As mentioned above, additional fiber precursor material can be optionally flowed so that a desired diameter is maintained while generating the desired length of the fiber. In an embodiment, multiple posts or similar structures can be used.

In an embodiment, the magnet and the post are disposed on the same structure or a different structure. In an embodiment where the magnet and the post are on the same structure, the structure can be moved to cause the fiber to wrap around a portion of the post.

In an embodiment, the magnet and/or post can be moved so that fiber extends from the post back towards the magnet so that the fiber length extends from the magnet to the post, is wrapped around a portion of the post, and extends back toward the magnet. In an embodiment, this process can be continuous so that a longer fiber can be produced. Example 1 provides additional details regarding this process.

In an embodiment, the magnet can include a permanent magnet, DC electromanget, AC electromagnet, and the like. In an embodiment, the strength of the magnet used can be adjusted as needed based, at least in part, upon the magnetic moment of the magnetic fiber precursor material. In an embodiment, the strength of the permanent magnet can be about 0.1 to 0.7 T.

In an embodiment, the fiber precursor material can include a polymer dissolved in a solvent to form a polymer mixture. In a particular embodiment, the fiber precursor material (e.g., magnetic fiber precursor material) can include a polymer dissolved in a solvent to form a polymer mixture, and the polymer mixture is mixed with magnetic particles. In addition, the fiber precursor material (e.g., magnetic fiber precursor material) can include one or more dopants.

In an embodiment, the polymer can include polymers that can be used in electrospinning as well as other polymers that are not compatible with electrospinning (e.g., solvent compatibility). In an embodiment, the polymer can include polymers such as: nylons, polyethylene, polystyrene, polylactide, polyglycolide, polypropylene, polyacetylene, polyphenylene vinylene, polypyrrole, polyesters, polyurethanes, polycaprolactone,polyethylene oxide, polyacrylonitrile, combinations of these, and blends of these. In an embodiment, the polymer can be about 10 to 60 weight percent of the magnetic fiber.

In an embodiment, the solvent that can be used includes those used in electrospinning as well as other solvents that are not compatible with electrospinning (e.g., low dielectric constant). In an embodiment, the solvent can be a low dielectric constant solvent such as water, chloroform, cyclohexane or tetrahydrofuran. The phrase “low dielectric constant solvent” means a solvent that has a dielectric constant of less than about 10.

In an embodiment, the magnetic particle can exhibit an effective magnetic moment, μ_(eff), greater than zero. In an embodiment, the magnetic particle can be superparamagnetic, paramagnetic, or ferromagnetic. In an embodiment, the magnetic particles are suspended in a solvent (e.g., water, chloroform, cyclohexane or tetrahydrofuran.) forming a magnetic fluid (also known as a “ferro-fluid”). An embodiment of the magnetic particle can include magnetic particles that have a diameter less than the diameter of the fiber, while in some embodiments the diameter of the magnetic particle is a factor of about 2 to 10 smaller than the diameter of the fiber. In an embodiment, the diameter (or longest dimension if the particle is not spherical) can be about 1 nm to about 500 nm. In an embodiment, the amount of magnetic particles included in the fiber can be 0 to about 80, about 0.01 to 80, or about 20 to 80 weight percent of the fiber. The type, concentration, and/or dimensions of the magnetic particles can be selected and/or adjusted, at least in part, based on the polymer, the strength of the magnet, distance between the aperture and the magnet, and the like.

In an embodiment, the magnetic particle can include: Fe₃O₄; Fe₂O₃, Ni, Co, Nd₂Fe₁₄B, SmCo₅, Al_(x)Ni_(y)Co_(z)Cu_(a)Ti_(b)Fe_(c), with x, y, z, a, b, and c such that the composition has about 8-12 weight percent of Al, about 15-26 weight percent of Ni, about 5-24 weight percent Co, about 0-6 weight percent of Cu, about 0-1 weight percent of Ti and the remainder to complete 100 weight percent in Fe, or a combination thereof. In an embodiment, the magnetic particle can be a paramagnetic metal coordination complex such as [Cr(NH₃)₆]Br₂, (NH₄)₂[Mn(SO₄)₂], (NH₄)[Fe(SO₄)₂], or VO(acac)₂.

As mentioned above, the fiber precursor material (e.g., magnetic fiber precursor material) can include one or more dopants. In an embodiment, the dopant can include one or more of the following: phosphorescent material, fluorescent material, SWCNT, MWCNT, hexagonal BN nanotubes, graphite, graphene, graphene oxide, silica, TiO₂, organic UV filters, proteins, cells, peptides, stem cells, therapeutic agents, and a combination thereof. In an embodiment, the amount of dopant included in the magnetic fiber can be about 1 to 70 weight percent of the magnetic fiber. Examples 1 and 2 provide additional details.

In an embodiment, the method can also include dispensing another material(s) from a another aperture(s) of the device so that the fiber precursor material is adjacent the other material(s). In an embodiment, the method can also include dispensing a secondary material from a second aperture of the device so that the fiber precursor material is adjacent the secondary material. The fiber precursor material and the secondary material can contact one another and optionally interact (e.g., react or cause a reaction) with one another. For example, the device can include two syringes where the tips are positioned so that as the material exits the syringe, the materials come into contact with one another. In another embodiment, the syringe can include an inner lumen and an outer lumen, where the exits of each lumen are substantially located at the some point. The fiber precursor material and the secondary material can be miscible or immiscible in one another. In an embodiment where the fiber precursor material and the secondary material are immiscible in one another, the materials can be easily separated once the fiber is formed. For example, a droplet of one material (e.g., including the magnetic particles) can be used to start the fiber forming process and then that material is no longer used. In this manner, the single droplet at the tip of the fiber can easily be removed.

In an embodiment, the fiber precursor material can flow past or through a cross-linking material towards the magnet. The cross-linking material cross-links the fiber precursor material as it is drawn so the fiber is formed during the drawing process. In an embodiment, the fiber can be magnetic, non-magnetic or a low magnetic fiber. In an embodiment, the fiber precursor material can include a component such as alginate, hexamethylene diamine or a combination thereof, while optionally including a magnetic particle as discussed herein. In an embodiment, the secondary material is a cross-linking agent such as a CaCl₂-water solution, sebacoyl chloride, hexane, and a combination thereof.

In particular, a two-droplet setup can be used to contact the magnetic fiber precursor material with a CaCl₂-water solution only during the fiber drawing stage, limiting the contact time between the two materials. The magnetic fiber precursor material, including Fe₃O₄, water, and alginate solution, is drawn through a droplet of CaCl₂-water solution as it is attracted to the magnet, thereby cross-linking the alginate and producing a non-magnetic or low-magnetic fiber.

In an embodiment, the secondary material can be a magnetic fiber precursor material. A drop of magnetic fiber precursor material is disposed with the fiber precursor material. In an embodiment, the fiber precursor material and the magnetic fiber precursor material are immiscible in one another. As the droplet of magnetic fiber precursor material is drawn to the magnet, the fiber precursor material is drawn with the magnetic fiber precursor material to form a fiber of the fiber precursor material. In an embodiment, the secondary material can be a polymer such as those described herein. In an embodiment, the magnetic fiber precursor material includes a magnetic particle and a solvent such as water and does not include a polymer of the secondary material. Once the fiber is formed, the portion of the fiber corresponding to the droplet of magnetic fiber precursor material can be removed.

EXAMPLES

While embodiments of the present disclosure are described in connection with the Examples and the corresponding text and figures, there is no intent to limit the disclosure to the embodiments in these descriptions. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of embodiments of the present disclosure.

Example 1 Brief Introduction:

A ferrofluid is a colloidal dispersion of stabilized magnetic nanoparticles that responds to an external magnetic field: above a critical field a pattern of sharp peaks is observed on the free surface of the ferrofluid. This instability is explored in this work in a new method for drawing polymeric nano and microfibers in which the magnetic force generated by a permanent magnet is used to draw fibers with controlled diameters in the 0.05-20 μm range. The magnetospinning technique demonstrated here is capable of producing nano and microfibers that are magnetic-particle-free, highly loaded with magnetic particles, porous and composite made of various polymers, biopolymers, and materials with a low dielectric constant, e.g. Teflon©. Finally, a magnetospinning two-droplet set-up provides broad possibilities to realize reactive spinning of fibers when the fiber drawing and chemical kinetics are synchronized.

Due to the very high surface-to-volume ratio and the microstructure that can be controlled at the molecular level, nanofibers find applications in composite materials, catalysis, filtration, and biomedicine¹⁻³. Electrospinning methods are often used to draw nanometer diameter fibers by stretching small liquid droplets at high voltage. Electrospinning has become the major nanomanufacturing method of ultrafine polymer fibers and composite fibers including magnetic nanofibers for cancer treatment⁴, single-cell manipulation⁵, synthesis of magnetic nanofibrous scaffolds for bone regeneration⁶, controlled drug release⁷, design of magnetic grabbers⁸, preparation of films with electric and magnetic anisotropy⁹, and composites for high-performance water-treatment applications¹⁰. The method is especially useful because of the ability to vary the material properties and control the fiber diameter.

The electrospinning process is dependent on the dielectric properties of the solvent. For example, the electric field required to obtain steady jetting increases with a decrease in the dielectric constant of the polymer-solvent system¹¹. Polycaprolactone (PCL) solution fibers with diameters below 200 nm can be electrospun only when the dielectric constant of a solvent satisfies ε_(r)>19. Below this value, the resulting fibers have diameters in the micrometer to millimeter range. Consequently, this limitation precludes the use of many polymer-solvent combinations for electrospinning nanofibers. Electrospinning of many biopolymers cannot be realized without blending with another polymer¹²; similarly, it is impossible to electrospin Teflon© nanofibers without using another polymer^(13,14). Further, reactive spinning when a diffusion-limited chemical reaction is used to synthesize or modify polymers in spinning solutions, cannot be realized by electrospinning due to the specific physics of the process. Alternatively, microfluidic spinning methods allow control over the fiber dimensions (from 50 nm to 100 μm) and reactive spinning, but the production rate is limited by the flow rate through the spinneret channel, so that scaling down to 30-150 nm fiber diameters becomes difficult because of the challenge to fabricate and operate small channels¹⁵. A new method of fiber spinning, magnetospinning, utilizes the stretching of ferrofluid droplets in a time-varying magnetic field, to fabricate nanometer diameter fibers in a simple set-up that is independent of the dielectric constant of the solvent and polymer used, can be used for reactive spinning, and can be scaled up and utilized for a wide range of materials and applications.

A ferrofluid is a surfectant-stabilized colloidal dispersion of magnetic nanoparticles suspended in a host fluid¹⁶. Ferrofluids behave as ordinary liquids at zero magnetic field and exhibit properties of solids when the magnetic field is applied. Instabilities of ferrofluids in an external magnetic field have been studied intensively for several decades¹⁶⁻²⁰. For example, when a magnetic field is applied perpendicular to a planar ferrofluid interface, conical shapes are observed on the surface. These spikes arise through energetically favorable balances between the magnetic force, gravity and surface tension¹⁶. Once the field is removed the interfacial deformation vanishes²¹. Though seemingly understood scientifically, this phenomenon has found limited applications^(16,22-24). This work demonstrates that when a magnet is brought close to a ferrofluid surface, below a critical distance the interface deforms to form a liquid bridge connecting the bulk fluid to the magnet. Under certain operating regimes the liquid bridge is stable, which allows a fine fiber to be drawn by moving the magnet away from the surface, and continual evaporation of the solvent establishes the final properties of the fiber.

Magnetic nanoparticles with an average diameter of 9±1.5 nm were synthesized by the co-precipitation method²⁵⁻²⁷. The particles were stabilized in chloroform by oleic acid and then mixed with polycaprolactone (PCL, see details in Materials and Methods section). The concentration of magnetic nanoparticles was 5.75 wt %. The suspensions are dilute and have a Newtonian shear rheology (constant viscosity) as reported in the measurements in FIG. 1J. Polymer-nanoparticle mixtures were characterized with an Anton Paar MCR 302 compact rheometer. The resulting ferrofluid is used to draw fine fibers (see FIGS. 1A-D). Here, a spherical or rectangular (about 25 mm in size) magnet is glued onto a rotating circular stage (diameter 84 mm), whose angular velocity is controlled with ±5 revolutions per minute (RPM) accuracy in the range of 50-1000 RPM. A syringe with a needle is connected to an automated pump and mounted on a 3D micromanipulator, which is used to maintain a precise distance of 6.5 mm between the tip of the needle and the magnet when the magnet passes the tip of the needle. As the magnet approaches the droplet (FIG. 1A) the magnetic force attracts the droplet (FIG. 1B). At a critical distance the droplet deforms and attaches to the magnet and a liquid bridge is formed (FIG. 1C). As the stage continues to rotate, a continuous polymeric fiber is formed via drawing by the magnetic force while the solvent evaporates and the final properties of the fiber are established. The fibers are collected between the magnet and a reel (e.g. post) glued on the opposite side of the stage (FIG. 1D). FIGS. 1G and 1H show a bundle of approximately 2500 nanofibers, produced in 5 minutes at 500 RPM with a rectangular magnet and three bent needles for collecting fibers.

Compared with commonly used spinning methods for nanofiber fabrication, magnetospinning set-up is very simple, safe and inexpensive. It can be assembled in any lab using standard lab equipment as shown in FIG. 1I. The method provides continuous fiber drawing, requires no high-voltage electric fields, and the results are independent of the electrical properties of the materials used. The shape of the magnet is not important in the magnetospinning set-up, but rather the gradient of the magnetic field generated. FIG. 1I shows a photograph of the magnetospinning set-up that can be assembled within minutes.

Three different magnetospinning regimes were discovered by varying the polymer concentration and the angular velocity of the stage, ω (FIGS. 2A-C), as indicated on the phase diagram (FIG. 2D). In the first regime, in part of the parameter space the droplet is able to transition to the magnet while retaining a connection to the main ferrofluid reservoir via a liquid bridge. As the magnet continues to rotate the liquid bridge is stretched and a fiber is produced. However, when the viscosity of the fluid is too low (second regime) the liquid bridge ruptures before a stable fiber is created (FIG. 2B), while in the third regime, when the angular velocity of the stage is too large the droplet is unable to overcome the viscous and surface-tension forces and cannot attach to the magnet (FIG. 2C). In both of these latter cases, the process boundaries prohibit nanofiber fabrication.

The magnetospinning limits are explained and identified in FIGS. 2A-G. The regime that enables a successful droplet transition from the syringe tip to the rotating stage will occur when the timescale of the rotating stage, 1/ω, exceeds the dynamic response timescale of the fluid droplet, R_(d)/v_(r), where R_(d) is the droplet radius and v_(r) is the fluid response speed. For an external magnetic force F_(m), is the estimated v_(r)=F_(m)/ηR_(d) where η is the fluid viscosity. For a spherical magnet of volume V_(m) and magnetization M, F_(m)˜3V_(d)μ₀χ/(χ+3)V_(m) ²M²/d⁷, where μ₀ is the permeability of free space, χ is the magnetic susceptibility of the suspension of nanoparticles, V_(d) is the volume of magnetic material contained within the droplet, and d is the closest separation between the fluid and the magnet¹⁶. Thus, the critical viscosity, η_(c), that admits a successful droplet transition will satisfy the inverse relationship η_(c)≦A/ω, where A=4πχφR_(d)μ₀V_(m) ²M²/((χ+3)d⁷) and φ denotes the volume fraction of nanoparticles. The susceptibility and magnetization are each known only up to an order of magnitude, with χ˜10⁻³ and M˜10⁶Am⁻¹; fitting the resulting curve to the data predicts χM²/(χ+3)≈6×10⁹A²m⁻², which provides a quantitative parametric prediction for the upper bound in the phase plane where nanofiber spinning is prohibited, which agrees well with the experimental results (FIG. 2D).

The location of the upper bound may be influenced by altering the concentration of nanoparticles within the fluid. An increase in the volume fraction of nanoparticles, φ, will increase the value of the parameter A in the relationship between viscosity and angular velocity. Assuming that variations in nanoparticle concentration do not affect the fluid viscosity, this implies that fibers with higher viscosities may be magnetospun by raising the concentration of magnetic nanoparticles (FIG. 2E). In addition, the parametric dependence of A on the magnetic susceptibility of the nanoparticles indicates that similar effects may be achieved by using nanoparticles composed of different elements, such as cobalt or nickel.

For the near-extensional flows characteristic of magnetospinning, we suggest that the lower bound in the phase diagram (dashed line in FIG. 2D) is limited by a critical viscosity of solution below which capillary breakup of a thread occurs. This observation is consistent with an entanglement concentration, C_(cr), since a stable jet of droplets is observed below that concentration²⁸. Using available data, this estimated critical entanglement concentration was C_(cr)=3.7% (FIG. 2H), which is in very good agreement with the experimental data.

Following the attachment of the fluid to the magnet, the continued rotation allows the liquid thread to be drawn out, which is accompanied by solvent evaporation and enables fabrication of magnetic fibers. Experiments were conducted for a range of stage rotation speeds to demonstrate the ability of magnetospinning to produce fibers with different diameters. The diameters of the fibers were estimated using SEM images and ImageJ software, and the diameter was found to decrease both with increasing speed of rotation and with decreasing PCL concentration (FIG. 2F). 50 nm in diameter nanofibers were formed. The error bars in FIG. 2F show the standard deviation for measurements of diameters of 50-70 different fibers produced in three independent experiments. In order to characterize the homogeneity of the fiber the measurement for two fibers along the 25 cm length of the fiber for two fibers (FIG. 2G) and had homogeneity for both fibers of 2.5-5%.

During magnetospinning, nanofibers were collected on the reels glued along the edge of the rotating stage. The length of one nanofiber in the set-up with stage radius R_(s)=42 mm is I=2πR_(s)=26 cm, so the magnetospinning set-up produced a 26 cm-long fiber with a single rotation. FIG. 1H shows approximately 2500 nanofibers, produced in 5 minutes at 500 RPM rate. In a scale-up experiment with three needles located along the magnet rotation, the production rate increased by a factor of 3, to 390 m/min.

The volume rate of production of fibers is given by V_(p)=πR_(f) ²[πR_(s)ωk₁k₂] where R_(f) is the fiber radius, k₁ the number of feeding needles, and k₂ the number of magnets on the stage. In FIG. 2I we plot a series of curves for the production rate of the magnetospinning method depending on the diameter of the produced fibers and diameter of the rotating stage. As can be seen from FIG. 2I, the productivity rate per nozzle in magnetospinning is comparable with electrospinning (V_(p)=0.04−0.2 cm³/h)²⁹. Scale-up of the system is possible by increasing the number of magnets and feeding needles at least to the density of one nozzle/cm, thus providing about 100 nozzles for an 80 mm-radius rotating stage, and two orders of magnitude increased productivity.

The physics of magnetospinning can be modeled by accounting for surface tension, evaporation and viscous effects in a stretching thread. We assume that the cross-sectional area of the fiber at each axial position (z) along the centerline is constant during the drawing process, so that the only time dependence in the set-up arises during the initial winding stage. We also assume that the fibers are slender, with radius R(z), where |dR/dz|<<1, with speed w(z), so that the process may be characterized by a classical extensional ‘Trouton’ model, including evaporation^(30,31):

$\begin{matrix} {{\frac{}{z}\left( {R^{2}w} \right)} = {{- \alpha}\; R}} & {{Equation}\mspace{14mu} 1\mspace{14mu} A} \\ {{{\frac{}{z}\left( {3R^{2}\eta \frac{w}{z}} \right)} + {\gamma \frac{R}{z}}} = 0.} & {{Equation}\mspace{14mu} 1B} \end{matrix}$

Here we assume that the evaporation rate is proportional to the exposed fiber surface, with a rate coefficient α. For the experiments conducted here, we measured α≈2×10⁻⁶ ms⁻¹. Also, z=0 is assigned to the position of the droplet at the pipette.

Three boundary conditions are required to solve the system represented by Equations 1A and 1B. We prescribe the droplet radius at the needle tip, R(0)=R_(d), and draw speed due to the stage rotation, w(d)=R_(s)ω. Finally, to close the system we assume that the velocity at which the fluid is drawn from the droplet to create the fiber is independent of rotation speed, so that w(0) is a constant for all experiments, which may be determined by matching to the experimental data. This approach provides the final fiber radius for a given operating regime. A study of equations 1A-B verifies that both the effect of surface tension and evaporation are necessary to explain the experimental observations in FIG. 2F. In the absence of evaporation, (1A) predicts a decrease in fiber radius with the inverse square root of the draw speed. In the presence of evaporation this effect is exacerbated further resulting in the potential for thinner fibers to be fabricated for equivalent draw speeds. The presence of surface tension in equation (1B) is essential to provide a dependence of the fiber radius on viscosity observed experimentally. When both of these effects are combined we are able to recreate the experimentally observed trends (FIG. 2F inset). In practice, additional measurements for a given experiment, such as the velocity at which fluid is drawn from the droplet and the particular behavior as the fiber solidifies and is wound onto the stage could be used to give a quantitative comparison.

Some biopolymers, for example alginate fibers, can be produced without blending with other polymers by wet spinning methods only, when the ion-cross-linker in the precipitation bath stabilizes the fibers. The unique possibilities of two-droplet set-up offered by magnetospinning can be demonstrated by the reactive spinning of alginate fibers. In particular, ordinarily non-spinnable polymers can be modified (cross-linked) within the characteristic time of fiber formation (FIGS. 3A-D) thus allowing for synchronization of fiber drawing and polymer cross-linking. For such a short characteristic time, diffusion-limited reactions can be used for reactive spinning. As shown in FIGS. 3A-D two droplets are pushed through the needle next to each other—one is filled with Fe₃O₄, water and alginate solution and the other is filled with CaCl₂-water solution (or other suitable cross-linking agent), where Ca²⁺ is a cross-linking agent for alginate (FIG. 3A). The magnetic droplet is attracted towards the magnet (FIG. 3B) and moves through the droplet composed of CaCl₂ solution (FIG. 3C). Ca²⁺ ions cross-link the alginate and as a result the polymer droplet can be stretched into a fiber (FIG. 3D). Using magnetospinning, fibers in the range from 5 to 200 μm in diameter were produced (see FIG. 1I for optical microscopy images of alginate fibers). In control experiments with only a magnetic droplet with alginate solution no fibers were formed; instead, droplets of polymer and magnetic particles jumped towards the magnet without forming a fiber.

The uniqueness of reactive magnetospinning refers to the specific physics of the process. If two reactive liquids are mixed prior to spinning, the time of contact between the two liquids is in the range of several seconds. Then, the length scale of diffusion is in the range of a millimeter, which dictates the scale of diffusion-limited reactions, so that a substantial fraction of polymer solidifies prior to drawing the fiber, which thus inhibits fiber formation. However, we have observed that using a two droplet set-up where the reactive liquids are in contact only during the fiber drawing stage makes fiber formation using the magnetospinning process possible. Our experiments demonstrate that the two droplet set-up in FIGS. 3A-D provides the possibility for transport of the ferrofluid droplet through the droplet with cross-linking Ca²⁺ ions, which avoids any prior contact between the liquids. Since the time of contact between the two liquids in our set-up is a fraction of a second the characteristic length scale of the reaction is in the range of tens of micrometers. This length scale is comparable to the fiber diameter generated in magnetospinning, prior to evaporation. Thus, the operating conditions of magnetospinning offer a range of time and length scales where diffusion-limited reactions can be utilized synergistically. The two-droplet set-up seems uniquely suited for magnetospinning because the magnetic field selectively attracts the magnetic liquid.

Even though many applications require highly loaded magnetic fibers^(4,8-10) it is advantageous to be able to produce fibers with lower loading of magnetic nanoparticles or even non-loaded fibers. The magnetic force withdrawing the droplet is dependent on the magnetic field gradient, and the concentration and magnetic properties of nanoparticles. By increasing the magnetic field gradient, we have found that the loading of magnetic particles can be decreased to 1 wt % magnetic nanoparticles dispersion. At this concentration no agglomerates of magnetic nanoparticles were observed at the surface of the fibers (FIG. 1E). It has also been shown that such particle concentrations do not change the mechanical properties of the fiber, and in some cases can even improve them³².

A comparison of coaxial (typically used for electrospinning) and two-droplet magnetospinning set-ups for reactive spinning is provided. For a coaxial nozzle geometry, two liquids (L1 and L2) are passed through the two needles (FIG. 3E). Diffusion of L1 into L2 starts inside of the needle with spacing a and continues in the Taylor cone (formed in the steady jet condition of an electrospinning process) of size b. For the typical flow rate for spinning 1 ml/h, a diameter of the needle 1 mm, the velocity of the fluid is about 0.35 mm/s. The minimum (at very small a) characteristic length for flow of two liquids in contact is estimated to be a+b≧2 mm. Thus, the interaction time of the liquids is about 6-10 s that is much longer than time of the fiber formation and flow. A diffusion coefficient in water for Ca²⁺ ions is 530×10⁻⁶ mm²s⁻¹, which yields a characteristic diffusion length of about >0.1 mm. Consequently, a large fraction of the polymer will be solidified even prior to the spinning.

For a two-droplet set-up (FIGS. 3A-D), the characteristic time of the two-liquid interaction during the stage of the liquid bridge formation is 3 ms (experimentally measured) plus the time of fiber drawing. The latter stage is defined by the magnet rotation speed, which in our experiments is in the range of 500-2500 RPM. The angular speeds result a contact time 0.1-0.01 s for the two liquids. This time scale corresponds to a characteristics reaction length for Ca +2 ions of 1-10 μm, which is comparable with the fiber diameter. Hence, the fiber drawing process is in agreement with chemical kinetics.

Thus, the physics of both processes is different: for electrospinning the time taken to flow from the tip of the needle to the tip of the Taylor cone is longer than the spinning process, and thus, fiber formation time is much shorter than the time of contact of two liquids. For a magnetospinning two-droplet set-up, the time of contact of two liquids prior to spinning is much shorter than the time of fiber spinning. This difference offers the possibility to realize reactive spinning with diffusion-limited kinetics, for example reactive magnetospinning of alginate fibers (FIG. 3F).

The magnetospinning method can also be used to produce magnetic-particle-free fibers (FIGS. 4A-D). Here, a droplet of PCL-chloroform solution is pushed through the needle using an automated pump. Then a droplet of Fe₃O₄ nanoparticles dispersed in water is added using a syringe connected to a second pump. Since water and chloroform are immiscible, there is no diffusion between these droplets (FIG. 4A). The coupled droplet is attracted by the magnet (FIG. 4B) and jumps towards the magnet, resulting in the production of a non-magnetic fiber (FIGS. 4B-C). High-speed imaging shows that after the magnetic droplet is attached to the magnet a fiber is drawn as the stage undergoes 4-5 subsequent revolutions, until all of the fluid in the droplet is stretched out into fiber form. This produces fibers of length 100-130 cm. Since the magnetic fluid and polymer solution are not miscible, the magnetic liquid is recyclable.

Polymers with low dielectric constant polymers cannot be electrospun but can be easily magnetospun, for example Teflon© fluoropolymer fibers that are ideal for the design of superhydrophobic materials. The electrospinning methods can produce only core-shell Teflon fibers with a shell made of polyacrylonitrile, PVDF and other polymer^(13,14) because Teflon© is soluble in liquids with very low dielectric constant (˜2). In contrast, here TAF 1600 (copolymer of 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole) in Fluorinert® FC-40 fluid (dielectric constant=1.9) was mixed with magnetic nanoparticles to magnetospin pure Teflon fibers with diameters ranging from 0.2 to 3 μm (FIG. 5A). These magnetospun nanofibers demonstrate excellent superhydrophobic properties (inset in FIG. 5A).

In addition, we used a range of polymers, including polyethylene oxide, polystyrene, and polymethyl methacrylate (PMMA) to fabricate nanofibers (FIGS. 5B-D), including nanocomposite fibers filled with silver nanowires (FIG. 5C) and multi-walled carbon nanotubes (MWCNT) (FIG. 5D). The resulting fibers are naturally ferromagnetic, but the iron oxide nanoparticles may be etched to create a porous non-magnetic fiber (FIG. 5B). Alignment of carbon nanotubes in polymeric matrices has attracted great attention due to dramatically increased tensile strength of the composite fibers³³. We have shown that magnetospinning is capable of producing highly loaded continuous nanofibers with aligned nanowires and nanotubes (FIGS. 5C, 5D). The demonstrated examples show that our method enables new opportunities to design nanostructured materials at the level of single nanoparticulates of different shapes and dimensions.

We have presented a new method for spinning of continuous micro and nanofibers using a permanent revolving magnet. The method utilizes magnetic forces and hydrodynamic features of stretched threads to produce highly loaded fine magnetic fibers and non-magnetic fibers. The magnetospinning process is independent of the solution dielectric properties and requires no high voltages. Scaling laws provide bounds for the operating regimes in which fibers may be fabricated, and theoretical models for the fiber drawing demonstrate the role of rotation speed, solution viscosity, evaporation and surface tension in the fabrication process. Magnetospinning is inexpensive, scalable, and simple, and the technique can be used for the reactive spinning and fabrication of composite magnetic and magnetic-particle-free fibers for a wide variety of applications. It is possible to build a magnetospinning set-up, such as that used here, within minutes by simply combining an inexpensive rotating motor and a permanent magnet.

Materials and Methods

Synthesis of nanoparticles: Magnetic nanoparticles were synthesized by the co-precipitation method²⁷. In the synthesis process, 1.625 g (8 mMol) FeCl₂.4H₂O and 4.43 g (16 mMol) FeCl₃.6H₂O were dissolved in 190 mL water at room temperature while stirring. 10 mL of 25 wt % ammonia was added into the solution, which led to the formation of black magnetite precipitate. After ten minutes of stirring the precipitate was magnetically separated from solution and washed three times by deionized (DI) water.

Magnetic nanoparticles stabilized in water: After the washing of magnetite nanoparticles with HNO₃ the precipitate was diluted to 100 mL with water and the pH raised to 2.5 with NaOH. 5 mL of a 0.5 M trisodium citrate dihydrate solution was added and the precipitate was stirred for 90 min while maintaining the pH close to 2.5 with hydrochloric acid. The precipitate was separated by applying an external magnetic field and the supernatant discarded. The precipitate was diluted to 50 mL with DI water and pH raised to 6.

Magnetic nanoparticles stabilized in chloroform: After washing in DI water, the magnetite nanoparticles were additionally washed two times with ethanol and three times with chloroform. This was achieved by sequential precipitation of nanoparticles with a magnet and re-dispersion of the precipitate in solvent by sonication. Following the final cycle of precipitation, in which the supernatant was removed, a few droplets of oleic acid were added to wet the precipitate and the mixture was sonicated for one minute with a high-power sonicator-homogenizer. The concentration of the magnetite nanoparticles was 11.5% by weight and was measured by complete evaporation of chloroform in a vacuum oven at 100° C.

Polymers in chloroform: Stock solutions of polystyrene (PS, molecular weight (MW) 280000 g/mol, Sigma Aldrich), polycaprolactone (PCL, MW 80000 g/mol, Sigma Aldrich) and poly(methyl methacrylate) (PMMA, MW 300000 g/mol, Sigma Aldrich) in chloroform. The stock solutions were used to prepare formulations for spinning comprising 6 wt % polymer and 5.75 wt % nanoparticles. The mixtures were used for spinning after 1-2 h mixing.

Poly(ethylene oxide) (PEO) in water/ethanol: PEO MW 400000 g/mol was dissolved in a mixture of water and ethanol (70/30) at 60° C. Mixtures for fibers spinning were prepared by mixing 14 wt % PEO solution and citrate-stabilized magnetite nanoparticles at a 1:1 ratio.

AgNW/PEO/MNP: Silver nanowires (Ag NW) with an average diameter of 90 nm and length of 20 μm provided by Blue Nano, USA were dispersed in chloroform at a concentration of 1.7%. Then 30 wt % solution of PCL, 1.7 wt % AgNW dispersion and 12 wt % dispersion of magnetite nanoparticles (MNP) were mixed in a 1:1:2 ratio. The spinning formulation contained 0.4 wt % AgNW, 5.75 wt % magnetite nanoparticles, 7.5 wt % PCL in chloroform.

MWNT/PEO/MNP in water: Multi-walled carbon nanotubes (MWCNT) were partially oxidized with a mixture of concentrated sulfuric and nitric acid (3:1 ratio) for 48 h at 80° C. The MWCNT were rinsed four times with water and three times with ethanol, and dried in a vacuum oven at 110° C. Following this, the MWCNT were re-dispersed to a concentration of 10% by weight in a citrate-stabilized magnetite nanoparticle dispersion using sonication. The obtained dispersion was stirred for one hour with 14 wt % PEO solution. The spinning formulation contained 5 wt % MWNT, 4.5 wt % magnetite nanoparticles, and 7 wt % PEO in water and ethanol (70:30).

High-speed imaging: Videos of the magnetospinning process were recorded on an Olympus i-SPEED FS camera at 10000 fps and analyzed with VirtualDub software.

REFERENCES

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Mapping the Influence of     Solubility and Dielectric Constant on Electrospinning     Polycaprolactone Solutions. Macromolecules 45, 4669-4680, (2012). -   12 Zhang, M. & Bhattarai, N. (US patent US20090087469 A1, 2009). -   13 Scheffler, R., Bell, N. S. & Sigmund, W. Electrospun Teflon AF     fibers for superhydrophobic membranes. Journal of Materials Research     25, 1595-1600, (2010). -   14 Muthiah, P., Hsu, S.-H. & Sigmund, W. Coaxially Electrospun     PVDF-Teflon AF and Teflon AF-PVDF Core-Sheath Nanofiber Mats with     Superhydrophobic Properties. Langmuir 26, 12483-12487, (2010). -   15 Jun, Y., Kang, E., Chae, S. & Lee, S.-H. Microfluidic spinning of     micro- and nano-scale fibers for tissue engineering. Lab on a Chip     14, 2145-2160, (2014). -   16 Rosensweig, R. E. Ferrohydrodynamics. (Cambridge University     Press, 1985). -   17 Butter, K., Bomans, P. H. H., Frederik, P. M., Vroege, G. J. &     Philipse, A. P. 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Example 2

Produced nanofibers can be used as scaffold for living cells and for tissue engineering applications. This example demonstrated that magnetic nanofibers are non-toxic for cells by growing fibroblast cells on magnetospun nanofibers. Cells also can be sprayed on the nanofibers during the magnetospinning process.

Cell Culture

The mouse NIH-3T3 fibroblast cells used for the present cultures were purchased from ATCC, USA. Dulbecco's Modified Eagle's Medium (DMEM) containing 10% (v/v) fetal bovine serum with antibiotics was used for cell growth on magnetic nanofibers. Cell cultures were maintained in a 37° C. incubator in a humidified atmosphere containing 5% CO₂. Cells were passaged at confluence using a standard trypsin protocol. Cells were washed twice and stored in PBS buffer. The 3T3 cells were seeded and cultured on the collagen-coated magnetic fibers in petri dish culture plates for 2 days. The cells were visualized (FIG. 5E) using the 488 nm laser of a Zeiss LSM 710 inverted confocal microscope with a ZSMmeta head (Welwyn Garden City, UK). The images were analyzed using Image Pro Plus.

It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a concentration range of “about 0.1% to about 5%” should be interpreted to include not only the explicitly recited concentration of about 0.1 wt % to about 5 wt %, but also include individual concentrations (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within the indicated range. In an embodiment, “about 0” can refer to 0, 0.001, 0.01, or 0.1. In an embodiment, the term “about” can include traditional rounding according to significant figures of the numerical value. In addition, the phrase “about ‘x’ to ‘y’” includes “about ‘x’ to about ‘y’”.

It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations, and are set forth only for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiments of the disclosure without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure. 

What is claimed is:
 1. A magneto-spinning apparatus, comprising a device that delivers a fiber precursor material, and a magnet positioned a distance from the device, wherein the fiber precursor material is drawn to the magnet to form a fiber. wherein the device is configured to deliver the fiber precursor material and a secondary material, wherein the device is configured so that the fiber precursor material and the secondary material are adjacent one another at a tip of the device.
 2. A method of forming a fiber, comprising: drawing a fiber precursor material from an aperture of a device towards a magnet positioned a distance from the aperture to form a fiber; dispensing a secondary material from a second aperture of the device so that the fiber precursor material is adjacent the secondary material; moving the magnet to extend the length of the fiber; moving the magnet so that the fiber wraps around a portion of a post positioned a distance from the magnet; and moving the magnet, post, or both so that the fiber extends from the magnet to the post, is wrapped around a portion of the post, and extends back toward the magnet.
 3. The method of claim 2, wherein the secondary material is a cross-linking agent.
 4. The method of claim 3, further comprising: drawing the fiber precursor material through the cross-linking material towards a magnet positioned a distance from the aperture to form the fiber, wherein the cross-linking material cross-links the fiber precursor material.
 5. The method of claim 4, wherein the fiber is a non-magnetic or low-magnetic fiber.
 6. The method of claim 3, wherein the cross-linking material is selected from the group consisting of: a CaCl₂-water solution, hexamethylene diamine, and a combination thereof.
 7. The method of claim 2, wherein the fiber precursor material includes a component selected from: alginate, sebacoyl chloride, hexane, and a combination thereof.
 8. The method of claim 6, wherein the cross-linking material is CaCl₂-water solution and the fiber precursor material is alginate.
 9. The method of claim 2, wherein the secondary material is a magnetic fiber precursor material, wherein the secondary material and the magnetic fiber precursor material are immiscible in one another, wherein as a droplet of magnetic fiber precursor material is drawn to the magnet, the secondary material is drawn with the magnetic fiber precursor material to form a fiber of the secondary material.
 10. The method of claim 9, wherein the secondary material is selected from the group consisting of: as nylons, polyethylene, polystyrene, polylactide, polyglycolide, polypropylene, polyacetylene, polyphenylene vinylene, polypyrrole, polyesters, polyurethanes, and a combination thereof.
 11. The method of claim 2, wherein the fiber precursor material includes a polymer dissolved in a solvent to form a polymer mixture, and the polymer mixture is mixed with magnetic particles.
 12. The method of claim 11, wherein the polymer is selected from the group consisting of: nylon, polyethylene, polystyrene, polylactide, polyglycolide, polypropylene, polyacetylene, polyphenylene vinylene, polypyrrole, polyester, polyurethane, polycaprolactone, combinations of these, and blends of these.
 13. The method of claim 11, wherein the magnetic particles exhibit an effective magnetic moment, μ_(eff), greater than zero.
 14. The method of claim 11, wherein the magnetic particles are selected from the group consisting of: Fe₃O₄; Fe₂O_(3;) Ni; Co; Nd₂Fe₁₄B; SmCo₅; Al_(x)Ni_(y)Co_(z)Cu_(a)Ti_(b)Fe_(c), with x, y, z, a, b and c such that the composition has about 8-12 wt % of Al, about 15-26 wt % of Ni, about 5-24 wt % Co, about 0-6 wt % of Cu, about 0-1 wt % of Ti and the remainder to complete 100 wt % in Fe; [Cr(NH₃)₆]Br₂; (NH₄)₂[Mn(SO₄)₂]; (NH₄)[Fe(SO₄)₂]; VO(acac)₂; and a combination thereof.
 15. The method of claim 14, wherein the diameter of the magnetic particle is less than the diameter of the magnetic fiber.
 16. The method of claim 11, wherein the magnetic particles are in a magnetic fluid.
 17. The method of claim 11, wherein the fiber has a diameter of about 50 nm to 20 μm.
 18. The method of claim 11, wherein the solvent is selected from the group consisting of: water, chloroform, ethanol, cyclohexane, tetrahydrofuran and a combination thereof.
 19. The method of claim 11, wherein the solvent has a low dielectric constant.
 20. The method of claim 2, wherein the fiber precursor material includes a dopant, wherein the dopant is selected from the group consisting of: a phosphorescent material, a fluorescent material, a SWCNT, a MWCNT, hexagonal BN nanotube, graphite, graphene, graphene oxide, silica, TiO₂, an organic UV filter, a protein, a cell, a peptide, a stem cell, a therapeutic agent, and a combination thereof. 